Conventionally, materials for coating particles are thermoplastics which are attached or adhered to the particles by a process involving immersion of particles in a solution of the thermoplastic material. A sufficient amount of the thermoplastic material to coat the particles is dissolved in a low-boiling point, water-immiscible solvent. The particles are suspended in water to form a slurry, and the solution of thermoplastic material is then added to the slurry. The resulting mixture is then stirred vigorously and slowly heated to drive off the solvent. As the solvent is removed, the water keeps the particles in the stirred suspension separated while the thermoplastic material is precipitated onto the surface of the particles. Finally, the coated particles are removed from the suspension by filtration and are dried.
Some disadvantages of the conventional coating method are: (1) The conventional thermoplastic coatings are subject to creep and abrasion, so their integrity may be compromised; (2) The solvents which dissolve thermoplastics may be toxic or otherwise environmentally undesirable; (3) Although most of the solvents can be recovered, trace amounts may remain to contaminate the water used as the suspension medium, necessitating its disposal as hazardous waste; and (4) The process may not be used to coat water-reactive materials.
The novel methods disclosed here overcome these disadvantages of conventional coating methods. In the disclosed methods, the particles to be coated are suspended in the presence of both an N3-terminated compound, conventionally referred to as an azido-terminated compound, and an R—C≡C-terminated compound, conventionally referred to as an ethynyl-(acetylene-) terminated compound. The azido-terminated compound and the ethynyl-(acetylene-) terminated compound are both adsorbed, absorbed, bonded, or otherwise disposed on or coupled to the surface of a particle, such that the azido-terminations and the ethynyl-terminations may be caused to react together to form triazole ring structures. The triazole rings link the two compounds together to form a thermosetting polymer composition coating the surface of a particle. The azido-terminated compound and the ethynyl-(acetylene-) terminated compound of the disclosed embodiments may each be small molecules, or large molecules such as prepolymers, or oligomers.
In the disclosed embodiments, the particulates may be slurried in a liquid dispersion medium comprising an organic solvent, an organic nonsolvent, or water. Accordingly, the particulate material is slurried in one of these media, and stoichiometric amounts, or other predetermined amounts, of both the azido-terminated material and the ethynyl-terminated material are added to the slurry in quantities sufficient to cover the surface of all the particles (i.e., the total combined surface area of all of the particles), or to cover a predetermined proportion of the total surface area, following which the stirred slurry composition is heated, with or without catalysts, to a temperature sufficient to induce formation of triazoles by reaction of the azido-terminated material with the ethynyl-terminated material. The curing reaction of the organic compounds into a thermosetting polymer is continued until polymerization is complete to form a thermoset coating on the particles. Embodiments of these processes or methods provide: (1) a coating that is a thermoset polymeric coating, less prone to creep or abrasion than are thermoplastic coatings; (2) the particulate slurry may be formed in either organic solvent, organic nonsolvent, a combination of solvent and nonsolvent as the solubilities and polarities of the azido- and acetylenic-terminated materials require, or water; (3) all of the organics may be recovered, and there is no solvent contamination of water; (4) for the coating of water-reactive and water-soluble materials which require a non-aqueous media for processing; and (5) for the coating of sensitive and/or reactive materials which require an aqueous media for processing. Particulates amenable to coating as disclosed here include the wide variety of materials susceptible to suspension in an organic solvent, an organic non-solvent, or water, including by way of example only and without limitation, materials such as metals, metal compounds, alloys, energetic compounds, energetic compositions, and those materials upon which a conventional thermoplastic coating may be applied.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments, which are illustrated schematically in the accompanying drawings and in the appended claims.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments, which are illustrated schematically in the accompanying drawings and in the appended claims.